The long-range goal of this research is to gain a better understanding of mechanisms that control vascular reactivity in the renal microcirculation by hormonal, paracrine and autacoid agents in health and disease. We will continue to focus our studies on regulation of vascular reactivity and receptor signaling pathways in the preglomerular vasculature. A unique combination of coordinated in vivo with in vitro approaches of overlapping themes is designed to gain insight into regulatory mechanisms responsible for renal vasoconstriction in young spontaneously hypertensive rats (SHR). Our previous studies indicate that excessive renal vasoconstriction is associated with the development of hypertension and is mediated by an abnormal balance of actions of vasoconstrictor angiotensin II (Ang II), vasopressin (AVP), and thromboxane (TxA2) and vasodilator systems (prostanoids, nitric oxide). In the proposed studies, we will characterize other vasoconstrictor systems, such as a-adrenergic nervous system and endothelin (ET), and the mechanisms by which they produce enhanced renal vasomotor tone in young SHR. We will test the central hypothesis that exaggerated vasoconstriction is mediated by direct actions of the constrictor agents on vascular smooth muscle cells, either alone, due to enhanced receptor density or postreceptor signaling, or in combination with a deficiency in the buffering capacity of vasodilator prostanoids. Specific aims are: I) Evaluate renal vascular reactivity in vivo to define the contribution of norepinephrine, ET, prostanoids and reactive oxygen species in exaggerated renal vasoconstriction in young SHR; II) Assess cellular signaling in vivo and in vitro to determine signaling pathways mediating actions of vasoconstrictor agents and mechanisms responsible for enhanced renal vasomotor tone in young SHR; III) Investigate in vivo regulation of Ang II, AVP, TxA2, a1-adrenergic, and ET receptors; and IV) Define the roles of tyrosine kinase and MAP/ERK kinase pathways to exaggerated renal vascular reactivity to constrictor agents in young SHR. We will evaluate key signal transduction steps from receptor mRNA expression and protein binding, and coupling with intracellular pathways to stimulate cytosolic calcium via mobilization and recruitment of entry channels. Our search for significant abnormalities in vascular actions should provide important new information that advances a more complete understanding of normal regulatory mechanisms and defects in controllers that may cause or contribute to the development of genetic hypertension.